Electric lamp and method of production



Amigo v 1968 T. H. ELMER ETAL 3,399J043 ELECTRIC LAMP AND METHOD OFPRODUCTION Original Filed Jan. 24, 1963 CLEAR COLORED CLEAR FIQE 1JNVENTORS Thomas H. Elmer Marfl'n E. Nordberg ATTORNEY United StatesPatent 3,399,043 ELECTRHC LAMP AND METHOD OF PRODUCTION Thomas H. Elmerand Martin E. Nordberg, Corning, N.Y., assignors to Corning Glass Works,Corning, N311, a corporation of New York @riginal application Jan. 24,1963, Ser. No. 253,681, now Patent No. 3,258,631, dated June 28, 1966.Divided and this application lien. 20, 1966, Ser. No. 521,911

7 Claims. (Cl. 65-30) ABSTRACT @F THE DTSCLOSURE A method of making animproved colored lamp envelope from a unitary non-porous 96% silicaglass by providing an envelope-shaped body of porous high-silica glass,dispersing an inorganic coloring agent in the pores of the body suchthat the inner surface of the body is free of coloring agent and thenconsolidating the body at elevated temperatures to form a nonporousstructure.

This is a divisional application of our copending application Ser. No.253,681 filed Jan. 24, 1963 which is now US. Patent 3,258,631.

This invention relates to electric lamps with particular reference tothe lamp envelope and its production. It is especially concerned with aconsolidated, high silica glass lamp envelope containing an inorganicadditive as a colorant.

Consolidated high silica glasses are well known under the genericcommercial designation, 96% silica glass. They are particularlycharacterized by high silica contents and consequent resistance tothermal deformation or breakage by thermal shock. Also, light absorbingimpurities are substantially removed during glass processing, and acontrolled amount of additive may be introduced by impregnation.

This type of glass is therefore particularly adapted to production oflamp envelopes and filters having pre-' scribed light transmittingcharacteristics, for example infrared heat lamps. An infrared lampoperates at a sufficiently high temperature to require the thermalresistance of a high silica glass envelope. The lamp envelope is furtherrequired to suppress total visible transmission below about 10%,transmit at least 50% in the near infrared, and provide apsychologically effective red color.

United States Patent No. 2,221,709 issued to Hood et al. describes basicproduction steps for producing consolidated high silica glasses and setsforth a family of particularly suitable parent borosilicate glasses.Briefly, the method includes: (1) forming or fabricating an article ofdesired shape from a parent borosilicate glass; (2) thermally treatingthe glass article at a temperature of 500 to 600 C. for a period of timeto separate the glass into a silica-rich phase and a silica-poor phase;(3) dissolving or leaching the silica-poor phase, usually with acid, toproduce a porous structure composed of the silicarich phase; (4)washing, to remove leaching residue, and drying; (5) thermallyconsolidating the porous structure into a non-porous vitreous article.Acid leaching of the phase separated glass leaves a highly siliceousstructure retaining its original shape and having a multiplicity ofintercommunicating submicroscopic pores. These are closed by thermalconsolidation without fusion to form a non-porous glass body ofcorresponding shape but smaller dimensions. Consolidation temperaturesare above 900 C. with about 12501300 C. being satisfactory for highersilica content glasses.

United States Patent No. 2,303,756 issued to Nordberg et a1. describes amodification of this glass forming technique. The porous glass isimpregnated with a solution of an inorganic glass-coloring agent, e.g.,a metal salt or other metal compound, and thereafter dried and heatedwithout fusion to close the pores and incorporate the metal ion of thecoloring agent within the glass body. For example, the desired deep redcolor in a heat lamp envelope is achieved with a combination of iron,nickel and aluminum salts which convert to the corresponding oxidesduring thermal treatment.

Recent evidence indicates that materials introduced into the glass byimpregnation in this manner may interfere with normal operation incertain types of lamps. In particular, there is evidence that additivessuch as iron or nickel oxides may react or combine with other lampparts, for example tungsten from the filament in an infrared heatinglamp, to produce an adverse effect on lamp operation and/or lighttransmission.

It has now been found that this situation can be satisfactorily remediedby providing a lamp envelope wherein color additives are excluded from athin layer on the interior surface. This layer need only be on the orderof 0.1-0.2 mm. thick, to be effective. The remainder of the envelope, orany portion desired, may be impregnated with additives in the usualmanner.

It has further been found that such partially impregnated envelopes maybe produced by modifying the conventional impregnation process. Inparticular, an envelope containing a solution at or near its inner glasssurface is selectively dried from the outer surface to insure a clearinner layer of glass. A further feature of the present invention then isprovision of a simple, commercially acceptable method of producing thenew lamp envelope.

The improved electric lamp of the present invention is characterized bya unitary consolidated high silica glass envelope, consisting ofintegral outer and inner sections, at least a portion of the outersection having a coloring agent incorporated therein to providesubstantially uniform light transmission characteristics, and the innersection being essentially free of the incorporated coloring agent. Theinvention further includes a method of producing such a consolidatedhigh silica glass envelope which comprises impregnating the outer layerwith a source of the glass coloring agent, providing an inner layeressentially free of coloring agent, and then firing the partiallyimpregnated envelope to a non-porous state.

The invention is further described with reference to the drawingwherein,

FIG. 1 is a side view, partly broken away, of an incandescent infraredheating lamp produced in accordance with the invention, and

FIGS. 2 and 3 are enlarged cross section views of lamp envelopesillustrating specific embodiments of the invention.

In FIGURE 1, incandescent, infrared heating lamp 10 has a tubular glassenvelope 12 composed of clear and colored sections as labeled. Itfurther includes a coiled tungsten resistance wire 14, terminating inenlarged straight portions 16, and external terminal members 18-1Sconnected to wire portions 16 by thin molybdenum foils 20 to whichenvelope 12 is sealed. The seal is a pinch seal or other known type ofseal employed between molybdenum foil and high silica or quartz-typeglass envelopes. Electrical connections are made to terminal members 18in accordance with conventional means not shown. Optionally, thintantalum supports may be provided to centrally position filament 14.

The selective impregnation feature characterizing the present inventionis illustrated in FIG. 2, a cross section view of an envelope such asenvelope 12 somewhat enlarged for purposes of illustration. As shown,the central colored portion of envelope 12 is composed of an externalsection 22 and an internal section 24. Section 22 has colorant oxidesdistributed throughout by impregnation with suitable salts followed bydrying and consolidation. In accordance with the present invention,internal layer 24 is maintained free of such additives. As describedlater, this may be accomplished by unilateral impregnation and/or movingthe solution inwardly into the glass from the internal surface of thetube during drying. Upon firing and consolidation, the clear innerportion 24 of the tube remains free of colorant or additive materials.

A porous glass envelope may be unilaterally impregnated by introducingimpregnating solution into the porous glass from the external or outsidesurface only. The porous glass envelope is provided with a stopper orcap at each end. It is then immersed in a suitable salt impregnatingsolution for a sufiicient time to permit the impregnating solution topenetrate from the outside surface into the porous glass to the depthdesired. The impregnated porous tube is then removed from the solution,rinsed to remove residual material from the surface, dried and fired inaccordance with conventional consolidation practice.

The required depth of penetration of the solution will depend onsolution concentration and density of color, that is light absorption,desired. It is convenient to impregnate only the outer half of theenvelope, that is to provide penetration of solution up to the centralleach plane of the tube. While some delay occurs in penetrating thisplane, the inner section may nevertheless be impregnated from the outersurface, if required. However, with solution near the inner surface,care must be taken to avoid additive being drawn to the surface duringdrying. To this end, it is desirable to leave the tube capped and dryfrom the outer surface only.

If desired, a glass envelope may also be impregnated from both surfacesin conventional manner. In such case, the envelope is immersed with theends open. After impregnation, the open ends are capped or stopperedduring drying, so that the envelope is dried entirely from the outsidesurface. With such unilateral drying, solution at the inner surface isdrawn into the interior to a sufiicient extent to provide the requisiteclear surface layer on consolidation.

The methods just described are particularly adapted to large volume,batch type operations where a plurality or bundle of tubes are immersedin a bath. In such an operation, impregnation must occur slowly toenable attaining relative uniformity of color in all envelopes despitetime variations in handling. Accordingly, it is desirable that theporous envelopes be immersed wet, since wet porous glass is impregnated,that is penetrated by solution, at a considerably slower rate than dryglass.

Alternatively, a porous glass tube may be rolled across a resilient,sponge-like surface containing the impregnating solution. Theimpregnating solution is picked up and drawn into the glass pores orcapillaries from the surface. The rolling is continued for suflicienttime to permit the desired degree or depth of impregnation. Thisprocedure is adapted to use on dry glass where faster impregnation isdesired and feasible. It is particularly convenient to use where asubstantial portion of the envelope is to remain clear or unimpregnated.

As shown in FIGURE 1, for example, end sections of envelope arecompletely uncolored and hence free of additive. This facilitates thetubulation and terminal sealing process. In the lamp of FIGURE 1, theclear sections correspond approximately to enlarged end portions 16 ofthe filament which run relatively cooler than the coiled portion andhence do not require color filtering.

By way of specific illustration, the invention is described withreference to production of a lamp envelope such as envelope 12 of FIGURE1.

A length of porous high silica glass tubing was produced in accordancewith procedures and materials generally described in previouslymentioned United States Patent No. 2,303,756. Tubing was drawn inconventional manner from a suitable borosilicate glass melt and heattreated at a temperature of 550 to 600 C. for sufiicient time toseparate the glass into a silica-rich phase and a silica-poor phase. Thesilica-poor phase was removed by acid leaching to provide a porousskeleton composed of the residual silica-rich phase and retaining theoriginal'tubular shape.

The porous tubing thus produced was provided with an inert plastic capover each open end. The cap extended a distance up the external tubewall coincident with the clear end portions shown in FIGURE 1. Thecapped tubing was immersed wet for about 35 minutes in an impregnatingsolution composed of a mixture of 300 grams each of iron, nickel, andaluminum nitrates dissolved in sufficient 0.1 normal nitric acid toprovide one liter of solution. This was sufficient to produceimpregnation just short of the inner surface in this tubing having a1.25 mm. wall thickness in the porous state.

The tubing was removed, thoroughly rinsed to remove residualimpregnating materials from the surface and dried by application offorced air to the tubing surface. The tubing remained capped duringdrying so that evaporation occurred from the outside surface only. Thedried tubing was heated in air to a temperature of about 850 C. at arate of C. per hour, then transferred to a vacuum furnace at 900 C.After a half hour hold to attain equilibrium, it was heated to atemperature of 1250 C. with hold times of one hour each at 950 C., 1000C., 1050 C. It was held for about a half hour at 1250 C. to insurecomplete consolidation of the impregnated porous glass to a non-porouscondition.

A luminous transmittance measurement was made through one wall of theconsolidated glass tube envelope, with an unfiltered photronic footcandle meter with a 2700 K. tungsten light source. The percenttransmittance was 4.5%. Visual examination of a cross section showed thetubing to be colored as in FIG. 3. An outer annular half 32 wasintensely colored. Inwardly from this was a lightly colored zone 34indicating a lower concentration due to the barrier effect along thecentral plane of the porous glass. Along the inner wall was a thin layerof clear glass 36, indicating no colorant additive.

A low water content in the glass is normally desired to enhance infraredtransmission and prolong filament life. For this purpose, the porousglass may be treated in an ammonium fluoride solution, in accordancewith the teachings of United States Patent No. 2,982,053, prior to beingintroduced into the impregnating solution described above. For example,porous tubing, as described above, was immersed in a 4% ammoniumfluoride solution for about two hours at room temperature andthereafter, while still wet, was impregnated with a nitric acid solutionof iron, nickel and aluminum nitrates and consolidated, as describedabove. In accordance with the patent teaching, infrared transmission at2.72 microns wavelength was greatly enhanced by the fluoride treatment,while luminous transmission was decreased to 2%.

Similar porous glass envelope tubes were impregnated with a 0.1 N nitricacid solution of grams each of iron, aluminum, and nickel nitrates perliter of solution for one hour. The tubes were impregnated from bothsurfaces, that is were uncapped during impregnation. They were thencapped and dried entirely from the outer surface with forced air asbefore. After consolidation as above, luminous transmittance through onewall was 2.2% as compared to 8.0% for a similar tube impregnated fromone surface only. Visual inspection showed a cross section as shown inFIG. 2.

The preceding description has been provided in order to illustrate apreferred embodiment and practice of the invention. Variousmodifications and alternative embodiments will be readily apparentwithin the scope of the appended claims. In particular, the invention isgenerally applicable to the production of lamp envelopes regardless ofthe particular impregnating materials introduced into the glass.

We claim:

1. A method of producing a unitary consolidated highsiliea glass lampenvelope comprising:

providing a porous, high-silica glass envelope-shaped body,

impregnating the pores of at least part of only an outer section of thewall of said body with a solution of an inorganic colorin agent, and

firing said body at elevated temperatures above 900 C. to consolidatesaid porous body to a non-porous envelope having a Wall characterized byan outer section containing said coloring agent and an inner sectionfree from said coloring agent.

2. The method in accordance with claim 1 wherein a solution of thecoloring material is introduced unilaterally from the outside surface ofthe porous glass body into the outer section thereof.

3. The method in accordance with claim 1 wherein a solution of thecoloring material is introduced unilaterally from the outside surface ofthe porous glass body into the outer section terminating at the centralplane of said body.

1. The method in accordance with claim 1 wherein a solution of thecoloring material is introduced unilaterally from the outside surface ofthe porous glass body into the outer section thereof such that the innersurface of the envelope is free from said coloring agent to a thicknessof at least 0.1 mm.

5. The method in accordance with claim 2. wherein the 6. The method inaccordance with claim 1 which includes the step of treating the porousglass body with an ammonium fluoride solution prior to introducing thecoloring material and firing the body.

7. A method of producing a unitary consolidated highsilica glass lampenvelope the wall of the envelope being characterized by an outersection containing an inorganic glass coloring agent and an uncoloredinner section which comprises:

impregnating the wall of a unitary porous, high-silica glass lampenvelope through both the inner and outer surfaces of said Wall with asolution of the salt of at least one inorganic coloring agent,

drying said envelope unilaterally from the outside surface to provide anouter section of the wall of the lamp envelope impregnated with coloringagent and an inner section of the wall which is essentially free fromsaid coloring agent, and

firing the impregnated envelope at elevated temperatures to consolidatesaid envelope, thereby converting said envelope from a porous to anon-porous state.

References Cited UNITED STATES PATENTS envelope is at least partiallyimmersed in a solution of DONALL SYLVESTER Pfimmy coloring material tointroduce the solution into a section from the outside surface only ofthe envelope.

E. R. FREEDMAN, Assistant Examiner.

